Signoes



March A. H. TAYLOR ET AL 1 8 HIGH FREQUENCY SIGNAL TRANSMISSION CIRCUITS Filed Oc't. 12, 1927 X 7'0 L0aa If f J Mf IV -c /7 ?f 226 T5 4 /Il INVENTORS A/berf H. ray/or,

A e o 76a. n3;

ATTORNEY.

Patented Mar. 8, 1932 a UNITED I LPOBATIOIN or CALIFORNIA nien FREQnENc sienan'ruansniss ou cinonlrs Application fi1ed ct0beri12,1927; serial-11 125323.

' inventionrelates-broadly to electron tubeamplifier systems and more particular 1y to a circuit arrangements for a high-power high frequency amplification system. 7 One of the objects of our 'invention is to provlde a circuit arrangement for a lngh power frequency amplifier system in which a'balanced operation of the circuits {may be 4 obtained without the establishment of parasitic oscillations in the tube circuits. r

"Another object of'o'ur invention is to provide a coupling system for the circuits of electron tubes wherein-the nodal points of the-signaling currents can be fixedin predetermined positions and oscillating" surgesin Opposition to normal amplification of the signaling currents avoided; I Our invention will be more clearly understood from the specificationhereinafter;fol-

lowing by reference'to theac companying drawings wherein? 1 I Figure -1 illustrate's the type of electron tube circuit to which. our invention may be applied Fig; 2: shows the application of the V 'circuitarrangement ofour inventionto the electron tube circuit of Fig. '1; Fig. shows J a coupling system of thetype to which the circuit of our invention may be applied; and Fig. 4:: illustrates thefapplication' of: our invention as a coupling system for a plurality of electrontubes in a high power highfrequency amplifier system. 1

In order to understandthe advantages 'of our improvedtype of balance circuit inits high internalcapacities and which are-to be operated at very high frequencies, it will be advisable to review briefly the behavior of older types of balance circuits and explain why'they fail towork onsuch'tubes and are are operated at a very high frequency;-

' Figure 1 shows a tube whichisf-balanced on itself by one of the methods already known to the art. The grid of this tube receives its excitation at a frequency, say F at thepoint marked EX. It is assumed that this excitation comes from a" master'os'cillator'of constant frequency, which mayor may not applieationjto tubes which have-"relatively unsatisfactory on all tubes-when such 'tub'es circuit of 'this tube istuned to resonance to i ALBERT H. rnYLon Ann no e. roundor.wasnines]:on, 3 mm. OEQOLUMIBIA, As- SIGNOBS, BY M'ESNE assremyxnn'rs, 'ro FEDERAL TELEGRAPH COMPANY, A 0012- the frequency F lo'r to 52 F 01 higherhar- Y 'monic frequencies ofthe excitation frequency.

:bymeans ofa variable-plate ircuit inductance and a'variable condenser C Means are'provi-ded for varying the number of plate turns, the number'offtuning turns and the fier tube of higher power or it 'may be an by means ofa variable balancing condenser point on the rplate'circuit coil system which B which connectshetweenthe grid and a 7 is .beloW ground-potential, .Whichmeans for practical purposes vbelow filamentpotential.

The voltage vin this lowerkport'ion of the coil V below the ground potential pointis in opposite phase tolthe voltage above this point,, and therefore, the internal'feed-back through the tube may be neutralized'by' adjusting the number of turns :below ground and by ad'- j usting the balanced condenser B The con.-

denser shown, at tvS 'is merely a stopping.

condenser of relatively large capacity. Now,

this: circuit has been persistently tried-:for 7 operation with tubes of 250 watt output and higher with very indifferent results whenthe 5d output frequency of said tubes is inexc'ess of 12,000 kcspand with no-apparent balance at all possible at frequencies between 16,000

cuit when in operation at veryjhighfrequen cies by means ofa voltage indicator instrument :of verylowf capacity shows jthat the coil-was explored several turns below: the connection which "leads to" filaments and ground. jAlth'ough this seems at first sur prisingyit is readily understandable-whenfit is considered that at these Very highffre quencies thet'otal number of turns in'that portionof thepl'ate coil system which is'tuned by the condenser C ',ris-re d'uced to sometimes as low as two turns, depending on the di'am I I 'eterof the 'co-il'system. For instanceg with a be piezo electrically controlled. The plate a coil about 2 /2*in diameter, /4 wide copper strap, turns separated about of an inch apart and using a 250 watt tube and op erating at 16,000 kcs. there are generally not over four turns in the tuned portion of the plate coil systems. In the case of the 1 k. w. air-cooled tube which has very high internal capacity there are about the same number of turns at the same frequency with straps "1 wide of even smaller inductance. It is, of course, impossible to wire these circuits up without having at least a good many inches of lead wire betweel the coil system and the ground andunder conditions like these, the actual nodal point does not lie in the coil system at all. On account of there being a very material drop of potential over 7 the ground'leads (leads to filaments) it might be considered that by adding a sufficient number of balance turns this difiiculty would be ultimately'overcome, but this has been found experimentallyto be fallacious, the reason being that after the first three or four turns there is so little coupling betweenthe added turns and the small number of turns in the tunable portionof the. coil that very little,

if any, electromotive force is produced in the turns.

balance turns after the first fewyturns. If, then, a reversed potential point cannot be found inthe first few turns which are in series with the balanced condenser, they will not be found at all. To put it another way, the positive drop in voltage over the inevitable ground lead cannot be overcome by the reversed potential existing in the balance turns connected through the balancing condenser 13 This difiiculty does not occur except at very high frequencies and it is a difficulty which is greatly aggravated by the use of tubes of large internal capacity, because the number of turns in coils which can be used in the tuned portion of the plate circuit is smaller with such tubes than with others, therebyreducing the coupling between tuned portions of the plate coil and the lower end of the coil which is used for balance This analysis of the situation agrees both with theory and facts as determined by experiments. i

Fig. 2 shows one method in which it has been possible to correct this inherent difficulty and extend this balance circuit to the operation of such high capacity tubes at very high frequencies. The modification is extremely simple but extremely important since it makes for the difference between success and failure in the operation of such tubes at such frequencies. In order to get more eflicient coupling with the balance turnsthe lower ter minal 10 of the condenser 0 is dropped below the lead 11 which goes to filaments and ground so that under these conditions neither side" of the condenser; C isfconnected to ground. Under these circumstances there is bound to be a nodal ,point of potential in th plate yst m .2. n 'the ba a e 1 eration can be carried out successfully. Fig. 3 shows one of the older methods of balancing an amplifier tube not against itself but against the next succeeding tube in the amplification system. A tube 14 excited at a very high frequency at the point EX is shown on the left of this diagram and a typical balance circuit connecting it with the succeeding tube 15 ofhigher power is shown to the-right. The plate coil system 12 of the left hand tube is shown with tap which leads through a stopping condenser S to the grid of the next amplifier 15 therebydelivering excitation voltage to that grid. To offset that portion ofthe energy which would pass through the internal coupling'of' the right hand tube 15 and thence, into the platecircuit. ofthe right hand tube 15, the-balance condenser, B is connected to a point below hand tube 1 1 and on the otherhand, to the plate of the right hand tube- 15. 1 There isa stopping condenser S of relatively large ca pacity in series with the balancevcondenser B but asfar as the electrical high frequency behavior of the circuit is con,cerned,., the balance condenser B may bezconsidered as connected directly toithe plate of the right hand tube 15. In the circuit of Fig. g itis assumed that it .is a straight balancepna iv n requency T er is no freq ncy doubling involved in this circuit as there-was in Figs. 1 andQ. Forth'e; purpose of illustrating our inventionit'maybe assumed that th e t hand, tube 1a i a 2 0-W t t bea d cooled tube or a water-cooled tube and that the excitation frequency developedinthe left hand tube ishigh, say in the; neighborhood of, for instance, 15,000, t 0;20.,, .(;),'0I kcs. The development of this frequency in the left hand tube 14 can be by a process of frequency ou but f o the ef h nd u ejthere is no further multiplication of frequency. The. excitation to they left hand tube might be, forinstance, 8,000 kcs. whereasthe plate circuit tunable 'by means of condenser C might bring out the second harmonic at 16,000 lrcs, but when the energy is taken voil from the coil system 12 to excite the right hand tube 15, the balance system must operate the right hand tube 15 at thesame frequency as the left hand tube; namely, at 16,0005ks. In other words, the right handtube is excited at the same frequency thatitputs out andis, therefore balanced at this frequency against the preceding tube. Now, this balanced circuit as shown inFig. 3 has been repeatedly tried withindiiferent results at 12,000 kcs. and, with absolute failure at higher, frequencies. It fails for exactly the same reason given for the failure of the circuit inFig 1; namely, that it is impossible to get a reversed potential across the balance condenser, B hic can u i ized, 9 n utralize th ene s mas-912' fed between grid and plate of the right hand tube. The method of correcting this difficulty is similar to the method followed in the other circuits as shown in Fig. 2.; namely, referringv now to Fig. 4,7the tuning condenser C; on-

the left hand tube has one terminal 10 brought below the terminal 11 which connects the coil system to filaments and ground, and this change makes again for the difference between failure andsuccess. A further exten:

sion of this principle is shown in Fig. 7-4; in the valve output circuits of theright hand tube 15. In Fig. 3theoutputcircuitof the right hand tube 15- is tuned by means of. a

condenser (3' which connects across certain turns of the plate coil syste1n 16 and the ground, but in Fig. t a similarcondenser (3' is connected across a portion of the coil 16, part of which lies above thelea-d 17 connecting the ground and filamentand part be;

low the connection point 17. This enables the balance system to be carriedthrough a succeeding or third power amplifiertube, or a connection to a load such as anantenna above the nodal point of the plate coil system 16 and at the same time a load such as a counterpose at a point below the nodal point of the;

plate coil system 16 may be provided, apro- 'cedure which is often useful in theart. It .should .be clearly understood that: these changes are very important as far as practical operation is concerned and vitally neces, sary. Itshould be understood that Figs. 1 and 3 have been illustrated only for purposes of clarification and comparison; j-The'new circuits of Figs. 2 and 4 have increased the availability of high power and all watercooled tubes forpower amplifier work'in the higher frequency band. The circuits of Figs. 2 and 1 are also a great advantage for tubes of low internal capacity in improving their performance.

The arrangement of the tap in the plate circuit inductance is such as to force a heavy circulatory current to come lower in the coil,

and such current is accompanied by a re-' verse potential with respectto the potential in the plate current inductance proper, thereby suppressing oscillatory currents. Both sidesof the tuning condenser are insulated from ground potential by the provision of the circuit arrangement shown, and-this condition facilitates tuning and adjustment of the circuits without shock 'to the operator.

The circuit arrangements described herein have been developed and tested under extended service condltions and have been found to give excellent results.

i' to While we have described the invention in its preferred embodiment'we desire that it be understood that modifications may be made and that no limitations upon the invention are intended other than areimposed byv the scope of the appended claims.v

What we claim as new and desire to secure byLettersPatentofgthe-United States is as follows:'-

lgA- transmission system for high 'frev uency currents comprising a plurality; of m I tubeand the input circuit of a succeeding electron tube, a connection. extending frorn the cathode electrode in the output circnit' f; H

one electron tube to a tap along saidinductance' 'intermediate -its; ends,- a variable fcapaclty" element having one side thereofncoin necte'd-to a-lpoint in said inductance on one sideof said tap and having-the opposite side thereof connected to a point in said 'induc otanceon'the'other'side of said'tap, said taps being disposed intermediate the ends of said V inductance, and a balancing circuit connect-' ed to said inductance at a point remote from" thepoint to which saidlast named-"side of ,said' variable capacity element is connected???" for stabilizing theoperation of thetransmis a P si'on system at high radio frequencies. 2. In a high frequency signal transmis'- sion system a plurality of electron tubes'each f having'grid, cathode and plate electrodes; an output circuit included between the'plate and cathode electrodes of each of"saidtubes,'an

input circuit extending between-the grid and cathode-electrodesjof each ofsaidtubes, an

inductance having portions thereof connected in common between the output circuit of one tubeand the input circuit of a succeeding tube,"the output circuit of'one tube terminat ing at a tappedconnection in saidind um tancelintermediate the ends-thereof, a vari'-.

ablecondenser system'havin'g one side thereof connected with said-"inductance at a posi-' tion on one side of said tappedconnectionthezother side of'said condenser system being;

connected: with said inductance at a position on theother sideof said tapped connection, and a balancing circuit connected to said inductance remote from the last mentioned side of saidvariable condenser "system and outside of the circuit formed through said condenser, for establishing a circulatory our rentpath in a direction opposite 'to the normal current flow accompanying the transfer of-ene'rgy from saidoutputcircuit to said input circuit and balancing the operation ofsaid circuits. 1

3. In a signal transmission system a plurality of electron tubes each having grid,

cathode and plate electrodes, an output cir-" o'cuit including the plate and cathode electrodes of oneelectron tube, an input circuit including the grid and cathode electrodes of j a succeeding electron tube, an inductance, a COIIIIBCtlOIl extending from the cathode electrode in said output circuit to a tap on said inductance intermediate the ends thereof, connections extending from said input and outputcircuits to points on said inductance, a tuned circuit comprising a portion of said inductance on one side of saidwtap and a portion onthe other side of said tap, and a balancing condenser, one side of which isconnected to said inductance beyondthe limits of said tuned circuit andthe other side of which is connected to the input circuit of said electron tube for opposing the tendency of said circuits to be set in a condition of parasitic oscillations. 1 1

4. In a signal transmission system, an electron tube having grid, cathode and plate electrodes a plate circuit inductance having a tap coupled to said plate electrode, a second tap on said inductance connected to said cathode electrode, a balancing condenser, a third tap on said inductance connected in circuit with said balancing condenser and said grid electrode, and a plate circuit tuning condenser connected in parallel with a portion of said plate circuit inductance by tapsthereto one of which is interposed between said plate circuittap and said cathode circuit tap and the other of which is on the opposite side-of said cathode circuit tap between the latter and said balancing condenser tap. v,

5. In a signal transmisison system, an electron tube having. grid, cathode and plate electrodes, an output circuit including the plate and cathodeelectrodes of said tube, an input circuit including the grid and vcathode electrodes of said tube, an inductance, aconnection extending from the cathode electrode in said output circuit to a tap on said inductance, connections extending from said input and output circuitsto-points on said inductance, a tuned circuit comprising in part an intermediate portion only of said inductance, part of which is ononeside of said tap and the other part of which is'on the other side of said tap, and a balancing condenser one electrodeof which is connected to said inductance outside of said portion comprising said tunedcircuit and the other electrode of which is connected to the input circuit of said tube for opposing the tendency of said circuits to be set in a condition of parasitic oscillation.

In testimony whereof weaffix our signatures. I r

i ALBERT H. TAYLOR.

LEO C, YOUNG.'. 

